Refrigeration system with distributed compressors

ABSTRACT

A refrigeration system for use with a building. The refrigeration system can include a plurality of refrigerated display cases, a condenser, a liquid main and a gas main. Each refrigerated display case can include an evaporator assembly and a compressor assembly fluidly coupled to one another. The condenser can be remotely located from the refrigerated display cases to reject heat from refrigerant in the system. The liquid main can fluidly couple an outlet of the condenser with the evaporator assembly of each refrigerated display case, and the gas main can fluidly couple the compressor assembly of each refrigerated display case with an inlet of the condenser. At least a portion of each of the liquid main and the gas main can be positioned adjacent each refrigerated display case to allow the refrigerated display cases to be positioned at a variety of locations within a shopping area of the building.

BACKGROUND

The present invention relates to refrigeration systems. Morespecifically, the present invention relates to refrigeration systems forrefrigerated display cases for displaying products in a commercialapplication.

A retail store, such as a supermarket, typically contains manyrefrigerated display cases for displaying and cooling food and/orbeverage items for sale. Many types of refrigerated display cases areknown in the art, and are in extensive use in retail locations. Suchrefrigerated display cases require a refrigeration system to maintain atemperature within the display case that is lower than ambienttemperature inside the store.

Refrigeration cycles are well-known in the art and generally include anevaporator, a compressor, and a condenser. A refrigerant fluid flowsfrom one component to the next, exchanging heat so as to absorb heatfrom a refrigerated area and reject heat at the condenser, typicallyexperiencing a phase change during the cycle.

A first prior art refrigeration system 20 is shown in FIG. 1. Therefrigeration system 20 includes refrigeration units 24 that are eachdedicated to a respective refrigerated display case 28. Therefrigeration unit 24 for each refrigerated display case 28 includes acompressor (not shown) and a water-cooled condenser (not shown). Thewater-cooled condenser is cooled by a coolant fluid, typically awater/glycol mixture that is provided by a closed coolant loop 32 withassociated coolant pumps 36. All the refrigerant for the refrigerationsystem is contained within the components of the refrigeration units 24,and a respective evaporator (not shown) in each refrigerated displaycase 28. Refrigerant fluid is heated and expanded in the evaporator asit removes heat from the refrigerated display case 28. The compressorcompresses the heated refrigerant and forces it to flow to thewater-cooled condenser in the refrigeration unit 24. The water-cooledcondenser transfers heat from the refrigerant fluid to the coolantfluid, allowing the refrigerant fluid to condense, pass through anexpansion valve, and return to the evaporator to be heated and expandedin a cyclical manner. The coolant pumps 36 in the closed coolant loop 32force the cooling water/glycol mixture to flow to the water-cooledcondenser from a heat exchanger 40 (e.g., an air-cooled fluid cooler),which is typically remotely located. At the heat exchanger 40, thecoolant fluid is cooled and then returned to the water-cooled condenserto receive heat from the refrigerant fluid.

A second prior art refrigeration system 44 is shown in FIG. 2. Eachrefrigerated display case 52 includes an evaporator 56 for removing heatfrom each refrigerated display case 52. Evaporated refrigerant is routedfrom the evaporators 56 via a suction header 58 to a local bank ofcompressors 60 and then through a discharge header 62 to a remotelylocated condenser 64 to be condensed. Condensed refrigerant is routedfrom the condenser 64 via a liquid header 57 to the evaporators 56. Thelocal bank of compressors 60 is located either at the end of a group ordirectly atop a group of refrigerated display cases 52 and containsseveral compressors connected in parallel within a sound-attenuatedcasing 66. The suction header 58 and the discharge header 62 arepartially located within the sound-attenuated casing 66. The dischargeheader 62 establishes fluid communication between the local bank ofcompressors 60 and the condenser 64 and is not necessarily positionedadjacent each refrigerated display case 52. Similarly, the liquid header57 establishes fluid communication between the evaporators 56 and thecondenser 64, and is not necessarily positioned adjacent eachrefrigerated display case 52. The local bank of compressors 60 serves tocompress heated refrigerant from several evaporators 56. The remotelylocated condenser 64 receives heated refrigerant from a single localbank of compressors 60.

A third prior art refrigeration system (not shown) is disclosed in U.S.Pat. No. 4,748,820. The third prior art refrigeration system includes abank of centralized compressors located in an “equipment room” of abuilding, remotely located from a group of refrigerated display cases.The bank of centralized compressors supply compressed heated refrigerantgas via a discharge line to a condenser typically positioned outside ofthe building. From the condenser, cooled liquid refrigerant is routedvia a liquid refrigerant line to evaporators positioned within therefrigerated display cases to cool a portion of each case. Theevaporated refrigerant gas is then routed to a local booster compressorand then back to the bank of centralized compressors in the equipmentroom via individual suction lines from each refrigerated display case torepeat the cycle. The individual suction lines converge prior to thebank of centralized compressors in an interstage manifold located in theequipment room.

SUMMARY

Some embodiments of the present invention provide a refrigeration systemincluding a plurality of refrigerated display cases. Each refrigerateddisplay case can include a dedicated evaporator assembly and a dedicatedcompressor assembly in fluid communication with each other. Eachdedicated evaporator assembly can be adapted to cool return air from therespective refrigerated display case by at least partially evaporating arefrigerant, and each dedicated compressor assembly can compressevaporated refrigerant from the respective dedicated evaporatorassembly. The dedicated compressor assemblies provide the only source ofrefrigerant compression in the refrigeration system. The refrigerationsystem can further include a gas main and a liquid main. The gas maincan fluidly couple an outlet of each dedicated compressor assembly to acondenser, which can be remotely located from the refrigerated displaycases to reject heat from the refrigerant to the environment. The liquidmain can fluidly couple an outlet of the condenser with each dedicatedevaporator assembly. The gas main and the liquid main can be positionedto allow refrigerant to flow between the condenser and the plurality ofrefrigerated display cases without pumping or compressing therefrigerant as it flows from the gas main, through the condenser, andinto the liquid main.

In some embodiments of the present invention, a refrigeration system foruse with a building is provided. The refrigeration system can include aplurality of refrigerated display cases located in a shopping area ofthe building. Each refrigerated display case can include an evaporatorassembly and a compressor assembly in fluid communication with eachother. Each evaporator assembly can cool return air from the respectiverefrigerated display case by at least partially evaporating arefrigerant. Each compressor assembly can compress evaporatedrefrigerant from the respective evaporator assembly. The refrigerationsystem can further include an air-cooled condenser that can be remotelylocated from the shopping area of the building to reject heat from therefrigerant. The refrigeration system can further include a liquid mainand a gas main. The liquid main can fluidly connect an outlet of theair-cooled condenser with the evaporator assembly of each refrigerateddisplay case. The plurality of evaporator assemblies can be connected tothe liquid main in parallel. The gas main can fluidly connect thecompressor assembly of each refrigerated display case with an inlet ofthe air-cooled condenser. The plurality of compressor assemblies can beconnected to the gas main in parallel. At least a portion of each of theliquid main and the gas main can be positioned adjacent eachrefrigerated display case to allow the plurality of refrigerated displaycases to be positioned at various locations within the shopping area.

Some embodiments of the present invention provide a refrigeration systemfor use with a building. The refrigeration system can include aplurality of refrigerated display cases positioned in a shopping area ofthe building. Each refrigerated display case can include a dedicatedevaporator assembly and a dedicated compressor assembly in fluidcommunication with each other. The dedicated evaporator assembly cancool return air from the respective refrigerated display case by atleast partially evaporating a refrigerant. The dedicated compressorassembly can compress evaporated refrigerant from the respectivededicated evaporator assembly. The refrigeration system can furtherinclude an air-cooled condenser positioned outside of the building toreject heat from the evaporated refrigerant in the system. Therefrigeration system can further include a liquid main and a gas main.The liquid main can fluidly connect an outlet of the air-cooledcondenser with each dedicated evaporator assembly. The gas main canfluidly connect each dedicated compressor assembly with an inlet of theair-cooled condenser. At least a portion of each of the liquid main andthe gas main can be positioned adjacent each of the refrigerated displaycases to allow the plurality of refrigerated display cases to beconnected to the liquid main and the gas main at various locationswithin the shopping area of the building. The liquid main and the gasmain can be positioned to allow refrigerant to flow between thecondenser and the refrigerated display cases without pumping orcompressing the refrigerant as it flows from the gas main, through thecondenser, and into the liquid main.

Other aspects of the invention will become apparent by consideration ofthe detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating a first prior art refrigerationsystem for refrigerating display cases.

FIG. 2 is a schematic view illustrating a second prior art refrigerationsystem for refrigerating display cases.

FIG. 3 is a schematic view illustrating a refrigeration system accordingto one embodiment of the present invention.

FIG. 4 is a detailed view of the refrigeration system of FIG. 3.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. Also, it is to be understood thatthe phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having” and variations thereof herein ismeant to encompass the items listed thereafter and equivalents thereofas well as additional items. Unless specified or limited otherwise, theterms “mounted,” “connected,” “supported,” and “coupled” and variationsthereof are used broadly and encompass both direct and indirectmountings, connections, supports, and couplings. Further, “connected”and “coupled” are not restricted to physical or mechanical connectionsor couplings.

FIG. 3 illustrates a refrigeration system 100 according to oneembodiment of the present invention for use with a building 120. Asillustrated in FIG. 3, the building 120 includes a shopping area 124. Asused herein and in the appended claims, the term “shopping area” refersto the commonly accessible area of a supermarket where customers maybrowse items for sale, and generally does not include any areasdesignated as equipment, storage, or maintenance areas.

The refrigeration system 100 includes refrigerated display cases 128.The refrigerated display cases 128 are positioned throughout theshopping area 124 of the building 120 for housing and displaying itemsto be refrigerated. The refrigeration system 100 includes a condenser132 located outside the building 120 remote from the shopping area 124,a receiver 136, a liquid main 140, and a gas main 144. The condenser 132may, in some embodiments, be located inside the building 120 but remotefrom the shopping area 124.

The receiver 136 is in fluid communication between the condenser 132 andthe liquid main 140, and is located substantially near the condenser 132outside the building 120. It should be understood by those of ordinaryskill in the art, however, that the receiver 136 can be located anywherealong the liquid main 140 between the condenser 132 and the refrigerateddisplay cases 128 (e.g., within the building 120) without departing fromthe scope of the present invention. Some embodiments may also includeindividual receivers located at each compressor unit, rather than onemain receiver. Further, In some embodiments, the refrigeration system100 does not include a receiver.

The condenser 132 has an outlet 148 in fluid communication with theliquid main 140. The condenser 132 also has an inlet 152 in fluidcommunication with the gas main 144. Each refrigerated display case 128is fluidly connected to the liquid main 140 via a liquid branch line156. The liquid branch lines 156 are fluidly connected to the liquidmain 140 in parallel with each other. Similarly, the refrigerateddisplay cases 128 are fluidly connected to the gas main 144 via gasbranch lines 160 in parallel with each other.

In some embodiments, the liquid main 140 and the gas main 144 are routedthroughout the building 120, such that at least a portion of the liquidmain 140 and at least a portion of the gas main 144 are positionedadjacent each refrigerated display case 128 of the refrigeration system100. Positioning at least a portion of both the liquid main 140 and thegas main 144 adjacent each refrigerated display case 128 allows therefrigerated display cases 128 to be installed at a variety of locationsin the shopping area 124 by tapping into the liquid main 140 and the gasmain 144 with a pair of respective liquid and gas branch lines 156, 160.In some embodiments, the liquid and gas mains 140, 144 may be outsidethe shopping area 124 adjacent a display case 128A that is near an edge(e.g., a wall) of the shopping area 124. In some embodiments, the liquidand gas mains 140, 144 may extend out into the shopping area 124adjacent each of a group of more centrally located display cases 128B.In still other embodiments, the store may be divided into “subloop”areas with a liquid and discharge main and air-cooled condenser for eachsub-area of the store. For example one set of liquid and gas mains withan air-cooled condenser for the left side of the store and a separateset of liquid and gas mains and separate air-cooled condenser for theright side of the store. A further embodiment may use such separatesubloops for different types of refrigerated merchandisers. For example,one set of liquid and discharge mains for the meat area, one set for theproduce area, etc. Thus, the liquid main 140 and the gas main 144 allowthe refrigerated display cases 128 to be positioned throughout theshopping area 124 of the building 120 in a variety of configurations,without requiring extensive routing of lengthy individual liquid and gasbranch lines 156, 160, and thereby minimizing the length of the liquidand gas branch lines 156, 160.

The arrangement of the liquid main 140 and gas main 144 throughout thebuilding 120 may simplify the installation procedure of refrigerateddisplay cases 128 or allow for the refrigerated display cases 128 to beeasily moved from one location to another within the building 120. Theliquid and gas mains 140, 144 may be plumbed into the building 120(e.g., under the floor or behind walls of the shopping area 124) beforeany refrigerated display cases 128 are installed. When refrigerateddisplay cases 128 are ready to be installed, they can be added to therefrigeration system 100 by tapping into the liquid and gas mains 140,144 at a location very near the desired location for the refrigerateddisplay case 128. This eliminates the need for routing lengthy liquid orgas branch lines 156, 160 between each of the refrigerated display cases128 and a centralized location, remote from the shopping area 124. Thisalso improves the modularity of the shopping area 124, in that therefrigerated display cases 128 can be reconfigured and moved throughoutthe shopping area 124 without requiring the cumbersome activity ofre-routing lengthy liquid and gas branch lines 156, 160.

In the embodiment illustrated in FIG. 4, the refrigerated display case128 includes an evaporator assembly 164, a compressor assembly 168, anda controller 172. (Alternate embodiments may also include an individualreceiver for each compressor unit) The evaporator assembly 164,compressor assembly 168, and controller 172 are dedicated to operateonly for the refrigerated display case 128. Specifically, a dedicatedcompressor assembly will only compress refrigerant received from anevaporator assembly of one refrigerated display case. The evaporatorassembly 164 can include one or more evaporators 173 to meet the coolingrequirements of the refrigerated display case 128. Similarly, thecompressor assembly 168 can contain multiple dedicated compressors 174.By way of example only, the illustrated refrigerated display case 128includes a compressor assembly 168 having two parallel dedicatedcompressors 174, and an evaporator assembly 164 having a singleevaporator 173.

The liquid branch line 156 connects the liquid main 140 to a refrigerantinlet 176 of the evaporator assembly 164. Prior to entering theevaporator assembly 164, the refrigerant will pass through an expansionvalve (not shown). In some embodiments, the refrigerant passes through aliquid subcooler which cools the liquid prior to entering the expansionvalve. A refrigerant outlet 180 of the evaporator assembly 164 isfluidly connected to an inlet 184 of the compressor assembly 168. In theillustrated embodiment, the evaporator assembly 164 includes a singlededicated evaporator 173. In embodiments employing more than oneevaporator, the evaporators of the evaporator assembly 164 can beconnected in parallel or series between the liquid branch line 156 andthe inlet 184 of the compressor assembly 168.

The evaporator assembly 164 is located such that air passing through theevaporator assembly 164 is discharged to a refrigerated area 198 of therefrigerated display case 128.

The gas branch line 160 connects an outlet 188 of the compressorassembly 168 to the gas main 144. The controller 172 in the refrigerateddisplay case 128 is electrically coupled to the compressor assembly 168.For example, in some embodiments, one or more of the dedicatedcompressors 174 has a variable capacity. The controller 172 can beelectrically coupled to the compressor assembly 168 to modulate thecapacity of the variable capacity compressor(s) 174 by adjusting, forexample, piston stroke or speed. In such embodiments, the controller 172can include automatic feedback control and/or can accept user input(e.g., from a keypad, a remote control, etc.). In some embodiments, thecontroller 172 may be located outside the refrigerated display case 128.In still other embodiments, one controller may serve more then onedisplay case and compressor unit.

Refrigerant flows, in liquid phase, from the receiver 136 to theevaporator assembly 164. At the evaporator assembly 164, heat istransferred from relatively warm air in the refrigerated area 198 torelatively cool liquid refrigerant, causing the refrigerant to evaporateinto a gas phase. The gaseous refrigerant is compressed in thecompressor assembly 168 as it flows out of the refrigerated display case128 to the gas main 144 via the gas branch line 160. The gas main 144carries the refrigerant to the condenser 132.

As shown in FIG. 3, the condenser 132 is air-cooled. A fan 199 forcescooling air across the condenser 132 to cool the refrigerant at leastpartially back to a liquid phase. The receiver 136 separates the liquidand gaseous phases of the refrigerant and supplies substantially liquidrefrigerant to the liquid main 140. In some embodiments of the presentinvention, the condenser 132 is the sole source of heat rejection fromthe refrigerant in the refrigeration system 100. In other embodiments, awater cooled condenser, or evaporative condenser may be used.

As shown in FIG. 4, the compressor assembly 168 for each respectiverefrigerated display case 128 is located within the refrigerated displaycase 128. In some embodiments, the compressor assembly 168 for eachrespective refrigerated display case 128 is located adjacent therefrigerated display case 128. In some embodiments, the compressorassembly 168 and the controller 172 are positioned adjacent therefrigerated display case 128 in a separate enclosure. In someembodiments, the compressor assembly 168 and the controller 172 can bepositioned directly adjacent an outer wall of the refrigerated displaycase 128.

In some embodiments, the multiple dedicated compressors 174 locatedwithin the compressor assembly 168 (in or adjacent each respectiverefrigerated display case 128) are the sole means for compressingrefrigerant in the refrigeration system 100. This provides a flow pathincluding the gas main, the condenser, and the liquid main, in whichthere are no active means for pumping or compressing the refrigerant. Insome embodiments, the multiple dedicated compressors 174 are oil freethereby doing away with oil distribution sub-systems and necessarycontrols.

In some embodiments, multiple dedicated compressors 174 are dedicated tothe refrigerated display case 128. It should be understood by thoseskilled in the art that multiple dedicated compressors 174 may bearranged in a variety of arrangements (e.g., parallel, series, back-up,etc.) while remaining within the scope of the present invention. Whenmultiple dedicated compressors 174 are used, the multiple compressors174 can be positioned within the refrigerated display case 128, adjacentthe refrigerated display case 128, or combinations thereof.

Various features and aspects of the invention are set forth in thefollowing claims.

1. A refrigeration system comprising: a plurality of refrigerateddisplay cases, each of the plurality of refrigerated display casesincluding a dedicated evaporator assembly adapted to cool return airfrom the respective refrigerated display case by at least partiallyevaporating a refrigerant, and a dedicated compressor assembly in fluidcommunication with the dedicated evaporator assembly to compressevaporated refrigerant from the dedicated evaporator assembly, theplurality of dedicated compressor assemblies providing the only sourceof refrigerant compression in the refrigeration system; a condenserlocated remotely from the plurality of refrigerated display cases toreject heat from the refrigerant to the environment a gas main fluidlycoupling an outlet of each dedicated compressor assembly to thecondenser; a liquid main fluidly coupling an outlet of the condenser tothe dedicated evaporator assembly in each of the plurality ofrefrigerated display cases, the gas main and the liquid main positionedto allow refrigerant to flow between the condenser and the plurality ofrefrigerated display cases without pumping or compressing therefrigerant as it flows from the gas main, through the condenser, andinto the liquid main.
 2. The refrigeration system of claim 1, furthercomprising a receiver positioned in fluid communication with the liquidmain to separate liquid and gaseous phases of the refrigerant and tosupply liquid refrigerant to each dedicated evaporator assembly.
 3. Therefrigeration system of claim 1, wherein each of the refrigerateddisplay cases includes a receiver in fluid communication with the liquidmain to separate liquid and gaseous phases of the refrigerant and tosupply liquid refrigerant to the dedicated evaporator assembly of thesame refrigerated display case.
 4. The refrigeration system of claim 1,wherein, the dedicated compressor assembly compresses evaporatedrefrigerant from the dedicated evaporator assembly of a singlerefrigerated display case.
 5. The refrigeration system of claim 1,wherein the plurality of dedicated evaporator assemblies is connected tothe liquid main in parallel.
 6. The refrigeration system of claim 1,wherein the plurality of dedicated compressor assemblies is connected tothe gas main in parallel.
 7. The refrigeration system of claim 1,wherein the condenser rejects heat from the evaporated refrigerant fromeach of the dedicated evaporator assemblies in the system to theenvironment.
 8. The refrigeration system of claim 1, wherein thededicated compressor assembly of each of the plurality of refrigerateddisplay cases is oil free.
 9. The refrigeration system of claim 1,wherein the condenser includes an air-cooled condenser.
 10. Therefrigeration system of claim 1, wherein the dedicated compressorassembly in at least one of the plurality of refrigerated display casesincludes at least two compressors.
 11. A refrigeration system for usewith a building, the refrigeration system comprising: a plurality ofrefrigerated display cases located throughout a shopping area of thebuilding, each of the plurality of refrigerated display cases includingan evaporator assembly adapted to cool return air from the refrigerateddisplay case by at least partially evaporating a refrigerant, acompressor assembly fluidly connected to the evaporator assembly tocompress evaporated refrigerant from the evaporator assembly; anair-cooled condenser remotely located from the shopping area of thebuilding to reject heat from the refrigerant; a liquid main fluidlyconnecting an outlet of the air-cooled condenser with the evaporatorassembly of each of the plurality of refrigerated display cases, theplurality of evaporator assemblies being connected to the liquid main inparallel; and a gas main fluidly connecting the compressor assembly ofeach of the plurality of refrigerated display cases with an inlet of theair-cooled condenser, the plurality of compressor assemblies beingconnected to the gas main in parallel, the liquid main and the gas maineach having at least a portion positioned adjacent each of the pluralityof refrigerated display cases to allow the plurality of refrigerateddisplay cases to be positioned at a variety of locations within theshopping area.
 12. The refrigeration system of claim 11, furthercomprising a receiver in fluid communication with the outlet of theair-cooled condenser to separate liquid and gaseous phases of therefrigerant and direct liquid refrigerant into the liquid main.
 13. Therefrigeration system of claim 11, wherein the plurality of compressorassemblies provide the sole source of compression for the refrigerationsystem.
 14. The refrigeration system of claim 11, wherein the compressorassembly of each of the plurality of refrigerated display cases is oilfree.
 15. The refrigeration system of claim 11, wherein: each of theplurality of refrigerated display cases is fluidly connected to theliquid main via a liquid branch line, each of the plurality ofrefrigerated display cases is fluidly connected to the gas main via agas branch line, and the liquid main and the gas main are positionedwithin or just outside the shopping area to minimize the length of theliquid branch lines and the gas branch lines, respectively.
 16. Therefrigeration system of claim 11, wherein the gas main and the liquidmain are positioned to allow refrigerant to flow between the air-cooledcondenser and the plurality of refrigerated display cases withoutpumping or compressing the refrigerant as it flows from the gas main,through the air-cooled condenser, and into the liquid main.
 17. Arefrigeration system for use with a building the refrigeration systemcomprising: a plurality of refrigerated display cases positioned in ashopping area of the building, each of the plurality of refrigerateddisplay cases including a dedicated evaporator assembly adapted to coolreturn air from the respective refrigerated display case by at leastpartially evaporating a refrigerant, and a dedicated compressor assemblyin fluid communication with the dedicated evaporator assembly tocompress evaporated refrigerant from the dedicated evaporator assembly;an air-cooled condenser positioned outside of the building, theair-cooled condenser positioned to reject heat from the evaporatedrefrigerant in the system; a liquid main fluidly connecting an outlet ofthe air-cooled condenser with each dedicated evaporator assembly; and agas main fluidly connecting an inlet of the air-cooled condenser witheach dedicated compressor assembly, the liquid main and gas main eachhaving at least a portion positioned adjacent each of the plurality ofrefrigerated display cases to allow the plurality of refrigerateddisplay cases to be connected to the liquid main and the gas main at avariety of locations within the shopping area of the building, theliquid main and the gas main positioned to allow refrigerant to flowbetween the condenser and the plurality of refrigerated display caseswithout pumping or compressing the refrigerant as it flows from the gasmain, through the air-cooled condenser, and into the liquid main. 18.The refrigeration system of claim 17, further comprising a receiverpositioned in fluid communication with the liquid main to separateliquid and gaseous phases of the refrigerant and supply liquidrefrigerant to each dedicated evaporator assembly.
 19. The refrigerationsystem of claim 17, wherein the plurality of dedicated evaporatorassemblies is connected to the liquid main in parallel.
 20. Therefrigeration system of claim 17, wherein the plurality of dedicatedcompressor assemblies is connected to the gas main in parallel.
 21. Therefrigeration system of claim 17, wherein the plurality of dedicatedcompressor assemblies provide the only source of refrigerant compressionin the refrigeration system.